The present invention relates to a process and equipment for carefully and accurately controlling the application of heat to plastic sheets. It even more specifically relates to the heating of plastic sheet material in high-speed packaging equipment, and is quite directly related to the heating of a plastic cover-carrier for a plurality of beverage containers.
It has been found desirable in the packaging of beverage containers, such as bottles or cans of beer and soft drinks, to carefully and accurately heat a sheet of plastic material which is then placed in position on an aligned collection of containers moving rapidly through a processing system.
As an example, in the processing of cans of beer, the brewery may, for example, supply the containers at an output speed of 1200 containers per minute. This discharge speed may range from a low level of 1200 containers per minute to a high level of 3,000 containers per minute.
As these containers are discharged from the "canning plant", they are placed upon a conveyor line which carries them to a packaging unit where they are packaged in trays or cases for delivery.
However, before being packaged, the containers are assembled into "packs" typically from 6 to 12 units each, and each of these "packs" desirably has a plastic carrier or protective cover placed thereover before the containers are placed into the case or tray.
The packaging machine for placing the plastic sheets upon the plurality of containers desirably has an idling speed of 50 cases per minute, but as the containers are discharged from the canning plant, they are directed by the conveyors into the packaging unit at speeds which range from 50 cases (of 24 containers) per minute (equal to the low bottling speed of 1200 containers per minute) up to 125 cases per minute at a top speed.
The speed at which these containers are brought to the packaging unit may vary as much as 1800 containers per minute (75 cases per minute), and in order that the packaging unit operates properly, and particularly that the heating elements therein which act upon the plastic sheets which provide the carrying or protective cover element operate properly, it is necessary to provide a heat/speed process control which has heretofore not been available to the industry.